Vehicles have been normally equipped with a radio, a cassette player or a CD (Compact Disk) player and speakers. Recently, more and more people want to equip with not only such audio equipment but also video equipment since they tend to enjoy movies or TV shows in their vehicles just like in their homes. Such a vehicle audio/video system typically includes a TV tuner, a VCR or a DVD (Digital Versatile Disc or Digital Video Disc) player and monitor screen for displaying video images. In a more sophisticated audio/video system, a navigation system is incorporated to provide both audio sound and video images as well as a route guidance function to guide a user to his/her destination.
FIG. 1 shows a typical example of audio/video system when it is installed in a dashboard 12 of a vehicle (the front passenger side is not shown). The audio/video system includes a display unit 11 which is normally placed about the center of the dashboard 12 and a DVD player 13 which may also include a TV tuner. If a navigation system is installed in the vehicle, the display unit 11 also functions as a monitor screen for the navigation system, and a driver is always allowed to watch the navigation status on the display unit.
However, because of the safety reason, while the vehicle is moving, the driver is not allowed by law to watch a movie, a TV program, a video game or any other moving images (hereafter “video”) which may distract the driver except for the navigation message or vehicle information. Namely, current traffic regulations for safe driving prohibit the display unit 11 from playing the video within the driver's view when the vehicle is in motion. To comply with this rule, a typical audio/video system includes an interlock function to disable a display unit under predetermined conditions. Such an interlock function checks the status of a footbrake and a handbrake (parking brake) to disable any video display unit. This feature is sometimes called a “brake interlock function”, the details of which will be described later.
FIG. 2A shows an example of the display unit 11 installed in the rear of a headrest 21 of a front seat or a middle seat. An interface cable 22 connects the display unit 11 and the DVD player 13 (or AV interface unit 47 shown in FIG. 4A). FIG. 2B shows another example of the display unit 11 which is installed in the rear of a seat 23 (front or a middle seat). Passengers in the rear seats or middle seats are always allowed to watch a video, since it will not directly affect the safe driving. Therefore, the brake interlock function for a display unit for rear seat passengers is not required but is required only for a display unit for a driver.
There are several types of audio/video system. The first type is an audio/video system only for a driver. As mentioned before, the brake interlock system is required for this type of system. The second type is an audio-video system only for passengers in the rear seats. This type needs not be controlled like the first one because passengers in middle seats or rear seats are always allowed to watch the video. Thus, the brake interlock function for the display unit is not required.
The third one is an audio/video system for both a driver and passengers, to which the present invention is advantageously applied. For this type, the brake interlock system is only required when a display unit is installed in the dashboard for a driver. On the other hand, the display unit should not be disabled when the display unit is installed for passengers in the rear seat or middle seat. This type of the audio/video system is preferable in terms of design and production cost because the same components such as display units can be used for a driver (front seat) and passengers (rear seat) except for the feature of the brake interlock function.
However, if a display unit can be used commonly for a driver's seat and rear passenger's seat, a vehicle must have a brake interlock function to disable the display unit for the driver when the vehicle is in motion. In contrast, when the display unit is installed for passengers in the rear or middle seats, such a brake interlock function should be released. In other words, the common display unit with the brake interlock function can be used for both a driver and a passenger if the audio/video system has a feature to release the brake interlock function when the display unit is installed for rear passengers.
FIG. 3 shows an example of the display unit 11 which can be used for both a driver and a passenger. Typically, the display unit 11 has a color LCD (Liquid Crystal Display) panel (screen) 11a. The display unit 11 has various buttons such as a power switch 11b, a volume up button 11c and a volume down button 11d, a select button 11e, and a display key 11f. For example, the volume up button 11c and down button 11d are used to adjust the sound volume or to adjust an image such as brightness, and the select button 11e is used to select an input source or a function for the display unit 11. The display button 11f is used to select a display mode such as “wide” or “normal” of the screen 11a. The display unit 11 is used either as a video screen or navigation screen. Namely, the select button 11e is used to choose an input source, a video from audio/video source such as a DVD or navigation data from the navigation system.
A wire 47a for releasing the brake interlock function comes with the display unit 11 when an end user purchases the display unit 11. The wire 47a is used only when the display unit 11 is installed at locations other than the front seat. In the case where the display unit is installed for rear seat passengers, the wire 47a is connected by a technician of a dealer to release the brake interlock function. Such a releasing procedure is done in accordance with instructions provided by a manufacturer of the audio/video display system. In other words, the user has to go to the dealer to activate the display unit for rear seat passengers.
FIG. 4A is an example of conventional audio/video system with the brake interlock function which can be used for both a driver (front seat) and a passenger (rear seat). In this example, the audio/video system is comprised of a display unit 11, a footbrake 44, a handbrake 45, an AV interface unit 47, a video source unit such as a DVD player 46, and a navigation system 48. Depending on the design of the system, the AV interface unit 47 may be formed within the housing of the display unit 11. The video source unit can be a TV tuner or a video game player instead of the DVD player 46. It is assumed that when two or more display units 11 are used, two or more AV interface units 47 will be provided corresponding to the display units so that each pair of display unit and AV interface unit can operate independently from one another.
In this example, both audio and video signals are sent from the DVD player 46 to the display unit 11 through the AV interface unit 47. The navigation data is also sent to the display unit 11 from the navigation system 48 through the AV interface unit 47. The display unit 11 has the select button 11e (FIG. 3) to select either a video screen or a navigation screen.
The AV interface unit 47 controls the brake interlock function in the audio/video system. The AV interface unit 47 monitors ON/OFF status of the footbrake 44 and the handbrake 45, and controls the display unit 11 to prohibit a driver from operating the DVD player or watching a video when the vehicle is running. Typically, the display unit 11 is designed to be used for both a passenger and a driver. If the display unit 11 is installed for a rear seat passenger, the brake interlock function must be released as noted above.
Also noted above, the wire 47a is used for releasing the brake interlock function. For example, the wire end is connected to the ground to release the brake interlock function. As a result, the AV interface unit 47 stops interlocking the DVD player 46 or display unit 11, allowing the passengers to watch the video when the vehicle is in motion.
Timing chart of FIG. 4B shows an example of brake interlock function as to how the display unit 11 is disabled or enabled in accordance with ON/OFF states of the foot brake and hand brake. In FIG. 4B, “Foot Brake ON” indicates that the footbrake is pressed, and “Foot Brake OFF” indicates that the footbrake is released. Further, “Hand Brake ON” indicates that the parking brake (handbrake) is used, and “Hand Brake OFF” indicates that the parking brake is released. “Display” indicates that the display unit 11 is either allowed or inhibited.
Suppose the vehicle is in motion, the display unit 11 is disabled (status 43a). The display unit 11 can be activated only when the vehicle is stationary. To show that the vehicle is in the stationary state, a driver must do the following steps. First, the driver presses the footbrake (status 41a) until the vehicle stops. Second, in the condition of pressing the footbrake, the driver activates the handbrake (status 42a) after the vehicle stops completely. Third, still in the condition of pressing the footbrake, the driver releases the handbrake (status 42b) and activates the handbrake again (status 42c). Fourth, the driver releases the footbrake (status 41b).
After all the above procedures of the footbrake and the handbrake, the brake interlock function is released (status 43b), thereby enabling the display unit 11. During this procedure, if the handbrake is released (status 42d), the display unit is disabled again (status 43c). The display unit is disabled without regard to whether the footbrake is activated or not (status 41c). If the handbrake is activated again, the display unit 11 is activated (status 43d).
Such a brake interlock function described above must be released when the display unit is used in the rear seat. To do this in the conventional technology, a user has to drive a car to a dealer to release this function. This is burdensome and time consuming to the user. Further, even if the law prohibits, a user may illegally use the wire to release the brake interlock function when the display unit is installed in the front seat. Therefore, it is necessary to establish a new method which can solve the above noted problems.